Protective arrangement



'Y April 24, 1928.

' LSGZEEZ H. s. HOLBROOK PROTECTIVE ARRANGEMENT Filed Feb. 11. 1926 Inventor:

Henry S. Hol brook.

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HENRY S. HQLB'RIOOK, OF RUGBY, ENGLAND, ASSZGNOR TO GENERAL ELEGTRIG COMPANY, A CORPORATIQN OF NEW YORK.

PROTECTIVE ARRANGEMENT.

a lication eiee February 11, 1926, Serial No.

My invention relates to protective arrangements for electric circuits, particularly to the circuits of electric traction systems which are especially subject to faults which throw 5 severe strains on the source of current sup- A. protective arrangement commonly employed in such systems comprises an inductive reactance inserted in the supply circuit 0 with an oil switch connected across the reactance to normally short circuit it. On the occurrence of a fault the switch is adapted to be tripped open leaving the reactance in the circuit to maintain the connection with 16 the source but limiting the current fiow therefrom. It has been found in practice that with this arrangement there is an objectionable burning of the contacts of the oil switch and throwing of oil from the same.

2G It is'an object of my invention therefore to provide an improved protective arrangement a of this nature by which may be obtained the protective advantages of the former arrangement with a reduction or elimination 26 of the disadvantages thereof.

Should one wish to employ a condenser alone to by-pass the current in the initial stages of the opening of the switch the enormous size of the condenser necessary to carry sufficient current would make it impracticable. A resistor used alone in shunt with the switch has the disadvantage of requiring more room than a reactor of the same impedance, is more costly, and dissipates more as energy, thus requiring greater ventilation.

In accordance with my invention I employ a current limiting means comprising a combination of a plurality of different kinds of impedance and normally short circuit this means by a switch which is adapted to be tripped open by a predetermined overload.

My invention will be better understood from the following description taken in connection with the accompanying drawing,

and its scope will be pointed out in the ap pended claims.

Referring to the drawing, Fig. 1 is 9. diagrammatic representation of one embodiment of my invention and Fig. 2 shows a modification thereof.

In the drawing, Fig. 1, the supply circuit 87,724, and in Great Britain February 14, 1925.

11 is connected to the contacts 12 normally bridged by the movable contact member 18 of the oil switch 14. The switch is held closed against the biasing spring 15 by the underset toggle 16 which is engaged by the lever 17. 1f the current in the circuit 11 reaches a predetermined value the overload relay 18 having its winding connected across the shunt 19 or, if preferred, in series with the secondary of a current transformer, closes its contacts, thus connecting the winding of relay 21 to a suitable source of current which may be supplied by the lines 22. The energization of relay 21 rotates lever 17 and thus trips the switch. Bridged across the contacts 12 of the switch is an inductive reactanc'e and a resistance comprised by the reactor and the resistor 24. @pening the switch 14 removes the short circuit across the reactor 23 and the resistor 24.

'1 he resistor 24: in this case will preferably be so proportioned that its resistance will be high enough to avoid the disadvantages as sociated with the use of a resistor only, but low enough to relieve the switch from the rise in voltage across it which occurs when an inductance alone is used.

in the modified form illustrated by Fig. 2 I have omitted the details of the switch and have shown its contacts bridged by a combination of inductance, resistance and capacitance comprised by the inductor 23, the capacitor 25 in series with the resistor 24 and the resistor 2 1 In this last form of my invention the capacitor will serve initially to by-pass some of the current and the resistor in parallel with it will help this action. The resistor in series with the capacitor will serve as a damping member to prevent any possibility of resonance between the reactor and capacitor at any of the frequencies set up by the 'arc discharge across the switch contacts, although it will delay slightly the by-pass ing of the current from the contacts of the switch.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. In combination, a circuit, a current limiting inductive reactance therein, a switch permanently connected across the reactance Q menace and arranged when closed to shunt the same, means responsive to a predetermined overin means responsive to a predetermined overload on the circuit for tripping open the load on the circuit for tripping open the switch, and means comprising a combination switch, and a resistance connected in shunt of resistance and capacitance connected in 6 with said reactance. a shunt with said reacta-nce.

2. In combination, a circuit, a current lim- In witness whereof, I have hereunto set 5 iting inductive reactance therein, a switch my hand this 27th day of January, 1926. permanently connected across the reactance and arranged when closed to shunt the same, HENRY S. HOLJBROOK. 

